1. Field of the Invention
This invention relates generally to electronic assemblies, and, more particularly, to arrangements of electronic assemblies for improving signal transmission.
2. Description of Related Art
Electronic assemblies are commonly manufactured in the form of circuit cards that plug into a backplane. Numerous electronic components are attached to each circuit card and are connected together via conductive traces or wires. Each circuit card generally has one or more connectors at one end, which mate with respective connector(s) on the backplane. Different circuit cards plug into different standard locations, or “slots,” of the backplane, substantially in parallel. The backplane is typically itself a circuit card, to which numerous connectors are attached for receiving circuit cards in different slots. The backplane generally includes traces or wires for establishing connections between circuit cards.
The circuit cards and the backplane are generally housed together within an enclosure called a “card cage” or “chassis.” In addition to the circuit cards and backplane, the chassis generally includes power supplies for energizing the circuit cards and air movers such as fans or blowers for cooling the circuit cards. The chassis also typically includes card guides, which form channels within which circuit cards can slide to ensure that they are inserted into backplane connectors with proper spacing and alignment.
We have recognized that many electronic applications involve drawing together large numbers of electronic signals from different locations, or “nodes,” and selectively switching the signals to various destinations. An example of this application includes computer networking systems, such as those managed by Internet Service Providers (ISP's). As is known, computer networking systems generally include a chassis having a backplane loaded with circuit cards and connected to the backplane in parallel, essentially as described above. The circuit cards include I/O cards (also called “line cards”) for accessing network nodes to send and/or receive network data. The circuit cards also include switch cards (also called “fabric” cards) for routing network data among the I/O cards.
I/O cards and switch cards generally operate together to route large amounts of network data simultaneously. To perform this role, network data arriving at an I/O card is generally conveyed to one or more switch cards via the backplane. The switch card(s) typically identify a destination, and they route the network data over the backplane to an appropriate I/O card.
We have recognized that the customary arrangement of parallel circuit cards plugged into a backplane has certain shortcomings when used in this and other applications. For instance, network data sent between I/O cards and switch cards can travel greatly varying distances depending upon the slots into which the respective cards are inserted. These different distances involve proportionally different propagation delays. Signals traveling greater distances are also subject to attenuation and possibly corruption due to conductive and/or dielectric losses. To minimize distances, the switch cards can be inserted into slots located toward the middle of the chassis (e.g., in slots 6 and 7 of a 13-slot chassis). Worst case backplane distances are then reduced by approximately one-half. The distances are still highly variable, however. In addition, as systems become faster, even these reduced distances present significant obstacles to throughput. Data rates exceeding 10 GBits/s are now common in the industry.
What is desired is an improved arrangement for further reducing worst case signal propagation distances and their variability.